One possibility is insect pests. Two tiny pests that can get into the house and attack seedlings are thrips and white fly. If you can, examine your leaves under magnification. I often take a picture with my camera and blow it up on my computer. A hand held magnifying glass will help. In any case, you should clean the leaves and stems with a damp soft cloth to remove any eggs or adults. You can also wash them with running water. Since they are seedlings, I would stay away from insecticidal soaps.
The other possibility is a nutrient balance. Plants that emerge from soil-less seed starter need to be transplanted to a potting mix when they get their first true leaves. At that point, the plant has exhausted the food in the seed and needs to get started photosynthesizing. I like to transplant after the first true leaves emerge.
Finally, make sure you let the plant dry before watering once it is out of the seed starter.
If none of these ideas work, I recommend you take a sample to your local Penn State Extension or send one to the Penn State Plant Clinic for analysis. Here is a link to the clinic.